In elevators, the counterweight and the car are interconnected with suspension ropes, which pass over a rotatable drive member. The rotatable drive member is usually in the form of a drive wheel. It is typically rotated with an electric motor. The rotatable drive member engages the ropes generally by friction and/or positive locking, whereby it can, by its rotation, make the ropes run from one side of the rotatable drive member to the other side thereof. The counterweight forms a force on the ropes on the counterweight-side of the rotatable drive member acting on opposite direction than the corresponding forces caused by the car on the car-side of the rotatable drive member. In some elevators the engagement between the ropes and the drive member is strong enough to support the whole weight of the car even without the effect of the counterweight. This may be the case for example if the frictional engagement between the ropes and the rotatable drive member is very firm or if the elevator uses toothed belts as the suspension ropes. An engagement this firm may be dangerous if for some reason the effect of the counterweight is lost. For example, if the counterweight is stuck immovable in the hoistway this causes a risk that subsequent lifting of the car upwards may result in a drop of the car when the engagement is ultimately is lost (stalling). In case the counterweight gets immovable, from thereon the rotation of the drive member to the car-upwards-direction will move the car upwards and wind slack rope on the counterweight-side of the drive member. Should the engagement in such a slack rope-situation be lost, the car would drop. In most elevators the counterweight and the car are furthermore interconnected with a compensation roping passing around a diverting wheel located in the lower parts of the hoistway. The compensation roping is generally enough to prevent the above described dangerous situation from developing. Elevators having a firm engagement between the drive member and the ropes and designed without a compensation roping passing around a diverting wheel located in the lower parts of the hoistway, on the other hand, are particularly vulnerable to dangerous stalling in such slack rope-situations. A problem with prior art elevators has been a lack of simple configuration for reacting quickly to counterweight-related safety issues.
In addition to stalling, also other kinds of counterweight-related safety issues may exist. Such issues may be for instance the danger of derailment of the counterweight and the activation of the safety gear of the counterweight. In prior art, counterweight-related safety issues have not been solved in a simple way.